Hume's Scepticism About Reason

39 HUME'S SCEPTICISM ABOUT REASON* Hume features an extended sceptical argument of apparently unlimited scope in the puzzling opening section of Book I, Part IV of the Treatise. He claims that our use of reason cannot even generate belief , much less knowledge. The argument is generally regarded as enigmatic if not downright embarrassing. Most of his recent interpreters, especially those who stress 'Hume's naturalism', avoid this section altogether. Those who do mention the argument describe it as "unsuccessful," "notoriously unclear," and "unpleasant." Even a sympathetic recent expositor calls it a "morass," while another commentator, obviously less sympathetic, regards the argument as "not merely defective, but one of the worst arguments ever to impose itself on a man of genius." This is unfortunate, for Hume's discussion in "Of Scepticism with Regard to Reason" fits into the general structure of the Treatise in ways that nicely "illustrate and confirm" the more familiar "preceding part of this discourse" (T 263). Hume intimates that it should do so as he moves to the last section of Book I, where he remarks that his "miscellaneous way of reasoning" in Part IV has "fully explain'd the nature of our judgment and understanding." Section I of Part IV should contain a significant part of that explanation . In this essay, I show that it does. On my reading, Hume's notorious argument turns out to be not only an integral part of his project, but a successful part of it as well. Section I vindicates the claims I think Hume made for it in his Abstract of the Treatise, that it give[s] us a notion of the imperfections and narrow limits of human 40 understanding. Almost all reasoning is there reduced to experience; and the belief, which attends experience, is explained to be nothing but a peculiar sentiment, or lively conception produced by habit. (A 657) 1. From Knowledge to Probability Hume's argument begins abruptly: "In all demonstrative sciences the rules are certain and infallible; but when we apply them, our fallible and uncertain faculties are very apt to depart from them, and fall into error" (T 180). This announces that the argument's focus is not on the proof procedures of the "demonstrative sciences" themselves, but rather on those who use them in hopes of acquiring knowledge. Hume reminds us of our fallibility, which we rarely consider when our concern is demonstrative reasoning. But as rationally reflective epistemic agents, we should take our fallibility into consideration whenever we produce a proof. We ought to consider not only the status of the rules of proof, we should also assess our ability to apply the rules correctly. To remind ourselves of our intellectual infirmities, we should try to "enlarge our view to comprehend a kind of history of all the instances, wherein our understanding has deceiv'd us ..." (T 180). We should recall those past times when we thought we had proved something and were wrong. This should lead us to be less confident that we have, on any particular occasion, actually produced a proof. As rationally reflective epistemic agents, we will -or should -- not be content to rest with our initial confidence. We should instead "... form a new judgment , as a check or controul on our first judgment or belief" (T 180). 41 This "new judgment" should also convince us to back off from our original confident claim to knowledge. We must realize that the exercise of reason alone does not insure its success. Even if there is nothing wrong with our faculty of reason as such, there are other factors which can and sometimes do intervene to flaw the result. We are not guaranteed truth or knowledge just because the objects of our inquiry are in the realm of the demonstrative. Instead [our] reason must be consider' d as a kind of cause, of which truth is the natural effect; but such-a-one as by the irruption of other causes, and by the inconstancy of our mental powers, may frequently be prevented. (T 180)' A perfect intellect might employ a set of rules infallibly. We aren't and don't. So we should only regard it as likely that our...